Is this feasible

There is no rail line to Courmayeur, the closest point would be Aosta, then a bus from there. It is a very long way around, mostly through Italy. Zermatt to Brig to Domodossola to Milan to Chivasso to Ivrea to Aosta, with only the Zermatt to Domodossola portion covered by the Swiss Travel Pass. Then there is the iffy cable car from Courmayeur to Mont Blanc (iffy because of seasonality, weather shut-downs, maintenance) then cable car to Chamonix, then train to Geneva. Or by bus Courmayeur to Chamonix, none covered by Swiss Travel Pass.

On the other hand, you can go from Zermatt to Chamonix more direct by rail and covered by Swiss Travel Pass. Visit Mont Blanc up and down via year round cable car. Shuttle van direct to Geneva, non of which is covered.

Thank you Sam. Guess Italy will have to wait. Sounds too confusing and too long a trip, and not enough time. My original plan was Zermatt to Mont Blanc via Mont Blanc express which I believe is covered by Swiss pass. Return same way but stop in Martigny to go to Geneva and think I’ll stick to that. Comments and suggestions welcome. Thank you. 😊

This map shows what is covered by a Swiss Pass: https://www.sbb.ch/content/dam/sbb/de/infotexte/uebersichtskarte-sts.pdf
Basically rail lines in Switzerland are covered, not in Italy or France.

The solid red lines on the map are rail lines which are covered by the pass (dashes, - - - - is a rail line in a tunnel, also covered, dots . . . . . is a line with a reduction only).
All the red lines have at least one train per hour.

Zermatt to Courmayeur (Aosta) doesn't look far in a straight line. Unfortunately the Matterhorn and a few other mountains are in the way.
The only way in or out of Zermatt is north down the valley Visp. And the only way into Italy in that area is the St Bernard Pass, road only.

As you can see, the line from Switzerland to Chamonix is covered. The direct line from Chamonix to Geneva is not, it is in France.